In video conferencing, two people communicate audio-visually. Each person is near a video conferencing terminal having a video display and a camera. The camera captures the image of the person, which is transmitted to the distant person. The image of the distant person is depicted on the display. Each person in the video conference is looking at his or her display. The camera is placed near the display. Since the user is looking at the display, the image captured by the camera is of the person looking away from the camera. Each person, is therefore, unable to maintain eye contact. Absence of eye contact during a conversation greatly reduces the effectiveness of communication.
Many prior art systems use two way mirror, also called half silvered mirror or beam splitter. A two-way mirror simultaneously reflects some light and passes some light.
FIG. 21 illustrates a prior art video conferencing system. A conferee 2102 views the display 2108 reflected in mirror 2104 while camera 2106 captures images of the conferee 2102. The image is captured from the same position that the conferee 2102 is looking at. Teleprompters function this way.
Another prior art video conferencing system uses a terminal equipped with beam splitter for reflecting an image generated by video display so that only the reflection and not a direct view of the display is seen by the conferee. The camera is positioned behind the viewing side of the beam splitter to capture the conferee's image through the beam splitter. The direct view of the display is blocked by an image blocking an image blocking film applied between the beam splitter and the display. Blocking the direct view of the video display greatly improves teleconferencing by eliminating the distraction of simultaneously viewing both the video display and the reflection of the display.
Prior art systems are quite bulky, especially when compared to modern display systems or modern teleconferencing systems. These systems waste a lot of energy, since a large amount of energy radiated by the displays is wasted since it goes through the two way mirror.
Many prior art systems compute a three-dimensional model of the conferee. Then the model is used to render an image of the conferee as if a camera were placed just behind the screen. The three-dimensional model is computed from multiple views of the conferee captured by cameras near the display, or by illuminating the conferee using light of a particular known pattern, and using the data pertaining to the illumination caused by the light.
In another prior art system, the three-dimensional model is not computed, but the final virtual view from the direction of the display is estimated by visual flow interpolation techniques. All these methods are computationally expensive. Furthermore, they do not perfectly capture the required image, but just estimate it. Also, the closer the viewer is to the display, the larger the disparity between the images captured by the various cameras, and harder it is to compute an accurate three-dimensional model of the conferee. Also, such approximation models falter under improper lighting conditions and improper viewing conditions such as presence of particulate matter or obstructions.
A prior art method for achieving eye-contact in a video conferencing situation uses a camera placed directly in the line of sight between the conferee and the display. Though a correct image of the user may be captured this way, the visual obstruction of the camera is not comfortable to the conferee.
An attachment mechanism removably secures the camera to a screen portion of a display screen such that the camera is disposed between the display screen and the conferee. The attachment mechanism can be a suction cup, strips of double-sided tape, or magnets. Magnetic force between the first and the second magnets removably secures the camera to a screen portion of the flat panel display.
Other prior art systems use projection systems and are bulky in nature. Furthermore, these systems do not offer complete isolation of the camera sensor from the light due to the display, causing unwanted glare. Also, in many situations flat panel displays are preferred to projection systems due to image quality reasons.
A typical display is made of a number of picture elements called pixels. In a transmissive display, a backlight is present behind the sheet of pixels. The backlight is illuminated by the light source along one or more of its edges. The backlight disperses the light into the pixels. Depending on the state of the pixels, the pixels emit light of different intensity.
A cathode-ray tube is used for displaying pictures and video on displays such as televisions, computer monitors etc. A cathode-ray tube has separate electron guns for different colors which are the sources of electrons. The electrons are directed to fall on a fluorescent screen, which causes the screen to emit light. Each electron gun is supposed to direct light only on a portion of display screen. Shadow masks and aperture grilles are provided to ensure that electrons from one electron gun do not fall on the portions of the display corresponding to other electron guns.
A plasma display is used widely for large television screens. The display is made of plasma pixels such that each plasma pixel consists of inert gases held between two plates. By directing high voltage across the pixel, the gas inside the pixel is converted to plasma state. This triggers the phosphor and light is emitted. Organic light emitting diodes (OLEDs) based displays are currently used in small-sized displays such as mobiles, personal digital assistants etc. OLEDs are light emitting diodes having an organic layer as a light emissive cathode layer. When the diode is forward biased, there is recombination of holes and electrons at the junction between the organic layer and the inorganic conductive layer. This recombination causes radiation in the visible region.
A liquid crystal display is one the most widely used displays today. The liquid crystal display is a transmissive display having a backlight, dispersing light from the light source into the liquid crystal sheet. The liquid crystal sheet itself is sandwiched between two polarizer sheets. The liquid crystal sheet comprises tiny liquid crystal cells forming pixels of the display. Depending on the electric voltage applied, the state of the liquid crystal changes. The light entering each cell is polarized by the first polarizer sheet and depending on the state of the liquid crystal, the polarization of the light going into the second polarizer sheet is modified. Hence, the intensity of light coming out of the sheet is controlled by the voltage applied across the liquid crystal. The pixel is black when the liquid crystal is in such a polarization state that the second polarizer blocks all the light coming from the liquid crystal. The pixel is white when the liquid crystal is in such a polarization state that the second polarizer allows all the light coming from the liquid crystal. By varying the voltage across the liquid crystal the pixel gray level intensity is changed. For many liquid crystals, the transition of the intensity of the pixel from one gray level to another is slow if the voltage difference required to make the transition is small. On the other hand, the transition of the intensity of pixel from white to black or black to white is faster as the voltage difference is larger.